In optical recording methods to record information on optical recording media by use of holography, the recording is typically carried out by way of causing interference between an informing light of substance light, having image information, and a reference light and writing the interference fringes on the optical recording media. The optical recording method is exemplified by those of Collinear system in which the informing light and the reference light are irradiated as a coaxial light beam. In the Collinear system, the interference fringes are formed by the informing light and the reference light to record image information etc. on the recording layer. Reproduction of the recorded image information etc. is carried out by way of irradiating the light same with the reference light to the recording medium from the same direction with that at recording, i.e. the light irradiation forms a diffracted light from the interference fringes and the information is reproduced though receiving the diffracted light.
When recording or reproducing the image information, the focus points are controlled in terms of the light beam irradiation, by way of focus control or tracking control, in order to adjust interlayer distances of recording layers in optical recording media and accident errors of optical recording and optical reproducing apparatuses and to record the information at normal positions of the optical recording media.
The method to control the focus points is exemplified by those of sampled servo system, in which a servo light is irradiated to the optical recording media for the focus control or the tracking control and the position information like focus information or track information is detected from the reflected light for the light irradiation. On the basis of the control of the focus points, the informing light and the reference light are irradiated at the normal positions of the optical recording media thereby the recording and the reproduction can be carried out (Patent Literatures 1 to 3).
The sampled servo system is exemplified specifically by the optical recording apparatus shown in FIG. 10. In the optical recording apparatus, a red light is used as the servo light, and laser lights of green etc. having a wavelength different from that of the servo light are used for the informing light and the reference light for recording.
The servo light, which being reflected at a dichroic mirror 13, passes through an objective lens 12, and irradiates an optical recording medium 21 so as to focus on the reflective film 2. The dichroic mirror 13 transmits the lights of green and blue wavelengths and reflects the light of red wavelengths. The servo light incident from a light entrance/exit surface A of the optical recording medium 21 is reflected by the reflective film 2 to emit again from the light entrance/exit surface A. The emitted return light passes through the objective lens 12 and is reflected by the dichroic mirror 13, and then a servo information detector (not shown) detects servo information. The detected servo information is used for the focus servo, tracking servo, slide servo and the like. The recording layer 4 is designed so as to be insensitive to red light.
The informing light and the reference light irradiate the optical recording medium 21 such that the informing light and the reference light, which being controlled into an appropriate position by the servo, transmit through a polarizing element 16, a half mirror 17, and the dichroic mirror 13 and form an interference image within an recording layer 4 by the objective lens 12. When the informing light and the reference light enter from the light entrance/exit surface A, they interact with each other at the recording layer 4 to form and record an interference image there, then transmit through the recording layer 4 and enter into a filter layer 6, and then, are reflected to turn into a return light before the bottom of the filter layer 6 without reaching the reflective film 2. The filter layer 6, which being a laminate of four layers of cholesteric liquid crystal, is designed to exclusively transmit red light.
In cases of optical recording apparatuses on the basis of the sampled servo system, however, only position information for light irradiation such as focus information and track information is detected in relation to the servo light, and the positions to irradiate the informing light and the reference light to the recording layer are controlled based on the results. Therefore, there arises such a problem that the reproduction is incorrect when there exists an accident error between the optical axis of the servo light and the optical axes of the informing light and the reference light, and also the optical recording apparatus for recording and the optical recording apparatus for reproducing are different each other. It may be possible to employ the sampled servo system for the informing light and the reference light in addition to the servo light in order to attain correct reproduction. When the sampled servo system is employed for the servo light as well as the informing light and the reference light in addition, however, there arises such a problem that the efficiency of recording/reproducing is lowered such as being inadequate for speeding up of the recording/reproducing. Since plural laser lights different each other are irradiated through different routes, it is necessary that layers such as wavelength selective reflective layers are laminated on the optical recording media depending on the respective laser lights, which leading to a problem of complicated layer construction.
Furthermore, recording capacity is limited in optical recording methods in which the recording light is moved on one plane horizontal to layer plane of the recording layer of the optical recording media to perform multiple-recording on the one plane.
Accordingly, such an optical recording method, an optical recording apparatus, and an optical recording medium have not been achieved yet that are excellent in providing higher efficiency of recording/reproducing and being uninfluenced by the mismatch of optical axes of plural laser lights induced from accident errors of optical recording and optical reproducing apparatuses when carrying out recording/reproducing or control of focus or tracking by use of a laser light, high multiple-recording can be performed, and also layer construction of the recording medium itself is simple, and their provisions are demanded currently.
Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2002-123949
Patent Literature 2: JP-A No. 2004-265472
Patent Literature 3: JP-A No. 2003-228875
The present invention aims to solve the problems in the art described above and to attain the objects described below. That is, it is an object of the present invention to provide an optical recording method, an optical recording apparatus, and an optical recording medium that are excellent in higher efficiency of recording/reproducing and being uninfluenced by the mismatch of optical axes of plural laser lights induced from accident errors of optical recording and optical reproducing apparatuses when carrying out recording/reproducing or control of focus or tracking by use of a laser light, high multiple-recording can be performed, and also layer construction of the recording medium itself is simple.